Renewable energy is energy derived from natural resources that can be replenished, such as sunlight, wind, rain, tides, and geothermal heat. The demand for renewable energy has grown substantially with advances in technology and increases in global population. Although fossil fuels provide for the vast majority of energy consumption today, these fuels are non-renewable. The global dependence on these fossil fuels has not only raised concerns about their depletion but also environmental concerns associated with emissions that result from burning these fuels. As a result of these concerns, countries worldwide have been establishing initiatives to develop both large-scale and small-scale renewable energy resources. One of the promising energy resources today is sunlight. Globally, millions of households currently obtain power from photovoltaic systems. The rising demand for solar power has been accompanied by a rising demand for devices and material capable of fulfilling the requirements for these applications.
Harnessing sunlight may be accomplished by the use of photovoltaic (PV) cells (also referred to as solar cells), which are used for photoelectric conversion (e.g., silicon photovoltaic cells). PV cells are relatively small in size and typically combined into a physically integrated PV module (or solar module) having a correspondingly greater power output. PV modules are generally formed from two or more “strings” of PV cells, with each string consisting of a plurality of PV cells arranged in a row and are typically electrically connected in series using tinned flat copper wires (also known as electrical connectors, tabbing ribbons, or bus wires). These electrical connectors are typically adhered to the PV cells by a soldering process.
PV modules typically further comprise the PV cell(s) surrounded by an encapsulant, such as generally described in U.S. Patent Application Publication No. 2008/0078445 (Patel et al.), the teachings of which are incorporated herein by reference. In some constructions, the PV module includes encapsulant on both sides of the PV cell(s). A panel of glass (or other suitable polymeric material) is bonded to each of the opposing, front and back sides, respectively, of the encapsulant. The panels are transparent to solar radiation and are typically referred to as the front-side layer and the backside layer (or backsheet). The front-side layer and the backsheet may be made of the same or a different material. The encapsulant is a light-transparent polymer material that encapsulates the PV cells and also is bonded to the front-side layer and the backsheet so as to physically seal off the PV cells. This laminated construction provides mechanical support for the PV cells and also protects them against damage due to environmental factors such as wind, snow and ice. The PV module is typically fit into a metal frame, with a sealant covering the edges of the module engaged by the metal frame. The metal frame protects the edges of the module, provides additional mechanical strength, and facilitates combining it with other modules so as to form a larger array or solar panel that can be mounted to a suitable support that holds the modules together at a desired angle appropriate to maximize reception of solar radiation.
The art of making PV cells and combining them to make laminated modules is exemplified by the following U.S. Pat. No. 4,751,191 (Gonsiorawski et al.); U.S. Pat. No. 5,074,920 (Gonsiorawski et al.); U.S. Pat. No. 5,118,362 (St. Angelo et al.); U.S. Pat. No. 5,178,685 (Borenstein et al.); U.S. Pat. No. 5,320,684 (Amick et al.); and U.S. Pat. No. 5,478,402 (Hanoka).
With many PV module designs, the tabbing ribbons represent an inactive shading region (i.e., area in which incident light is not absorbed for photovoltaic or photoelectric conversion). The total active surface area (i.e., the total area in which incident light is use for photovoltaic or photoelectric conversion) is thus less than 100% of the original photovoltaic cell area due to the presence of these inactive areas. Consequently, an increase in the number or width of the tabbing ribbons decreases the amount of current that can be generated by the PV module because of the increase in inactive shaded area.
To address the above concerns, PCT Publication No. WO 2013/148149 (Chen et al.), the teachings of which are incorporated herein by reference, discloses a light directing medium, in the form of a strip of microstructured film carrying a light reflective layer, applied over the tabbing ribbons. The light directing medium directs light that would otherwise be incident on an inactive area onto an active area. More particularly, the light directing medium redirects the incident light into angles that totally internally reflect (TIR) from the front-side layer; the TIR light subsequently reflects onto an active PV cell area to produce electricity. In this way, the total power output of the PV module can be increased, especially under circumstances where an arrangement of the microstructures relative to a position of the sun is relatively constant over the course of the day. However, where asymmetrical conditions are created by the PV module installation relative to a position of the sun (e.g., a non tracking PV module installation, portrait vs. landscape orientation, etc.), light reflection caused by the microstructured film may, under certain conditions, undesirably lead to some of the reflected light escaping from the PV module.
In light of the above, a need exists for a light redirecting film useful, for example, with PV modules in reflecting increased levels of incident light at angles within the critical TIR angle of the corresponding front-side layer.